int eb_is_valid(const eb_t p) {
eb_t t;
fb_t lhs;
int r = 0;
eb_null(t);
fb_null(lhs);
TRY {
eb_new(t);
fb_new(lhs);
eb_norm(t, p);
fb_mul(lhs, t->x, t->y);
eb_rhs(t->x, t);
fb_sqr(t->y, t->y);
fb_add(lhs, lhs, t->y);
r = (fb_cmp(lhs, t->x) == CMP_EQ) || eb_is_infty(p);
}
CATCH_ANY {
THROW(ERR_CAUGHT);
}
FINALLY {
eb_free(t);
fb_free(lhs);
}
return r;
}
int eb_upk(eb_t r, const eb_t p) {
fb_t t0, t1;
int res = 0;
fb_null(t0);
fb_null(t1);
TRY {
fb_new(t0);
fb_new(t1);
eb_rhs(t1, p);
if (eb_curve_is_super()) {
/* t0 = c^2. */
fb_sqr(t0, eb_curve_get_c());
/* t0 = 1/c^2. */
fb_inv(t0, t0);
/* t0 = t1/c^2. */
fb_mul(t0, t0, t1);
res = (fb_trc(t0) == 0);
/* Solve t1^2 + t1 = t0. */
fb_slv(t1, t0);
/* If this is not the correct solution, try the other. */
if (fb_get_bit(t1, 0) != fb_get_bit(p->y, 0)) {
fb_add_dig(t1, t1, 1);
}
/* x3 = x1, y3 = t1 * c, z3 = 1. */
fb_mul(r->y, t1, eb_curve_get_c());
} else {
fb_sqr(t0, p->x);
/* t0 = 1/x1^2. */
fb_inv(t0, t0);
/* t0 = t1/x1^2. */
fb_mul(t0, t0, t1);
res = (fb_trc(t0) == 0);
/* Solve t1^2 + t1 = t0. */
fb_slv(t1, t0);
/* If this is not the correct solution, try the other. */
if (fb_get_bit(t1, 0) != fb_get_bit(p->y, 0)) {
fb_add_dig(t1, t1, 1);
}
/* x3 = x1, y3 = t1 * x1, z3 = 1. */
fb_mul(r->y, t1, p->x);
}
fb_copy(r->x, p->x);
fb_set_dig(r->z, 1);
r->norm = 1;
}
CATCH_ANY {
THROW(ERR_CAUGHT);
}
FINALLY {
fb_free(t0);
fb_free(t1);
}
return res;
}
